For high integration of a semiconductor device, it is necessary to reduce the spacing between metal wirings (i.e. the spacing between local wirings, between global wirings, or between a local wiring and a global wiring). However, if the spacing between metal wirings is reduced, the wiring delay due to R (wiring resistance)×C (wiring capacity) will be dominant, whereby high speed operation of signals will be impaired. A schematic diagram showing a position for forming an interlayer insulating film of a semiconductor device, is shown in FIG. 1.
In order to solve such a problem, it has been attempted to reduce the wiring resistance or the wiring capacity, or both of them. For reduction of the wiring resistance, it has been studied, for example, to change the material from an Al material to a Cu material or an Au material which is a material having a lower resistance than the Al material. However, such a metal material is readily diffusible by the Si component of an Si chip, which brings about a new problem, such as necessity to form a barrier layer, which is now being studied.
On the other hand, for reduction of the wiring capacity, at the time of laminating the above metal wirings via an insulating layer so-called an interlayer insulating film, silica glass is usually employed as such an insulating film. However, with such an insulating film, the demand at present can not adequately be satisfied, and it has been proposed, for example, to further dope fluorine, to make the film porous, or to employ an organic insulating film.
For example, JP-A-1-235254 discloses a semiconductor device having metal wirings formed in multilayers via a porous insulating film, on a semiconductor substrate. This invention comprises depositing on a substrate an insulating film made of a mixture comprising a basic oxide such as sodium oxide or calcium oxide and an acidic oxide such as silicon dioxide or boron oxide, followed by heat treatment to precipitate or elute only the basic oxide or the acidic oxide to form pores in the film, whereby the reliability of the semiconductor device is substantially decreased by inclusion of e.g. the basic oxide.
JP-A-2000-21245 proposes a method for forming pores by using fine hollow polymer particles together with an organic silicon compound. However, use of an organic compound is insecure from the viewpoint of heat resistance and thus will substantially limit the process conditions in the subsequent process steps for the production of the semiconductor.
Further, JP-A-11-289013 discloses a method for forming a porous insulating film, which comprises evaporating metallic silicon in an oxygen-containing atmosphere. The insulating film formed by this method is one having a relative permittivity as small as at most 1.95, but in its film composition, SiO2 is the main component, as disclosed in paragraph 0052 in the publication as “SiO2 occupies the major portion, and the integral strength of the SiOx component is a few %, based on the entirety”. Further, the film structure is insecure with respect to the mechanical strength, since it is composed of a pile of granules, as is evident from FIG. 15 of the publication. Besides, the vapor pressure of metallic silicon is low, and for its evaporation, a high temperature and heat resistant jig may, for example, be required, and there will be a problem such that the vapor deposition time is long, and the productivity is low.
On the other hand, applications of the SiOx film include, for example, a reflection-preventing film and a gas barrier film, in addition to the above-mentioned interlayer insulating film. Especially, a plastic having the gas barrier property improved by vapor deposition of an SiOx film, is convenient as a packaging material for pharmaceuticals, food products, etc., since the contents can easily be ascertained. However, on the other hand, the SiOx film has a brownish color tone, and it is desired to improve the color tone.
Accordingly, e.g. JP-A-8-197675 proposes a method of coating hydrogen peroxide to an SiOx vapor deposition film, and it is disclosed that the method is effective for improving oxygen and steam permeability. However, if hydrogen peroxide is employed, it is necessary to clean it subsequently, and it is difficult to completely remove it from e.g. semiconductor devices. Further, in the same publication, it is disclosed that the light transmittance and the oxygen permeability of an SiO film on a plastic film, were improved by irradiation with light, but such an effect is merely at a level of a few %.
In view of the above, it is an object of the present invention to provide a low relative permittivity SiOx film which is excellent in heat resistance without using an alkali metal, fluorine or the like and undergoes little change with time to SiO2 and which is highly reliable as an interlayer insulating film for metal wirings, and a semiconductor device employing such a film.
Another object of the present invention is to provide an SiOx film having the relative permittivity further lowered and having the insulating property further improved by irradiating electromagnetic waves to the SiOx film to increase oxygen in the SiOx film.